In general, wiring boards are widely used as printed wiring boards that are mounted with electronic components and so on to form electronic devices. With the miniaturization of the electronic devices and so on, the printed wiring boards are also required to have higher accuracy and higher density. Normally, in the wiring board, copper is used as a wiring material and is formed into a predetermined pattern by electrolytic plating. As a method of forming a feeding layer in this copper wiring electrolytic plating formation, electroless copper plating is carried out after using a wet process as a pretreatment. Thereafter, the electrolytic copper plating is carried out using the electroless plating layer as a seed layer (feeding layer). The electroless plating has a problem that, as compared with the electrolytic plating, it is difficult to suppress variation in plating quality, a large amount of a chemical solution is required, and the number of required steps is large. In view of this, a method of forming copper of a seed layer by a sputtering process has been studied as a process that replaces the electroless plating.
However, there has been a problem that the copper formed by the sputtering process is poor in adhesion to an electrically insulating layer of a printed board, i.e. a thermosetting resin, and thus cannot be put to practical use.
In order to solve this problem, it has been proposed to form CuN as an adhesion layer under a copper seed layer which is formed by sputtering (Patent Document 1, Patent Document 2).